Earlier studies in this laboratory have shown that an 125I-labeled highly purified form of epidermal growth factor (EGF) did not cross the transplacental barrier when given intravenously to pregnant CD-1 mice. This finding supports that a complementary ligand for embryonic/fetal tissue EGF receptors may originate locally or intrinsically in the embryo. We are presently investigating this possibility with specific immunoassays for EGF and transforming growth factor (AlphaTGF), a polypeptide with essentially identical biological properties to EGF. In another study we are investigating reproductive tract tissues and kidney for the presence of proEGF. Pronounced localization of EGF immunoreactivity occurred in mouse kidney distal tubule cells only after treatment of the sections with pronase; this finding was compatible with the localization demonstrated by other investigators with 32P-cDNA probe for preproEGF mRNA by in situ hybridization experiments. We have demonstrated preproEGF mRNA by dot-blot hybridization in immature mouse uterus and in uteri of estrogen-treated ovariectomized mice. A pronase-dependent EGF-like immunoreactivity was also found in the luminal or epithelial region of uterine sections. We are currently exploring methods to extract and quantitate proEGF and ultimately determine what biological signals stimulate processing of this protein, especially in reprodutive tract tissues.